1. Field of the Invention
The present invention relates to an apparatus for removing sand and other debris from a wellbore; more particularly, the invention relates to apparatus and methods for use in a wellbore utilizing a venturi.
2. Background of the Related Art
In the production of oil and gas, sand breaks loose from oil producing formations and is carried into the wellbore with production fluid. As the production rate of oil increases, the formation sand which breaks loose and enters the wellbore also increases. Over time, the wellbore can become filled and clogged with sand making efficient production of the well increasingly difficult. In addition to sand from the formation, other debris including scale, metal shavings and perforation debris collects in the wellbore and interferes with production.
One method of removing debris from a wellbore involves the introduction of liquid which is circulated in the well. For example, liquid can be pumped down the wellbore through a pipe string and convey debris to the surface of the well upon return through an annulus formed between the pipe string and the wall of the wellbore. Nitrogen or some other gas can be added to the liquid to create a foam for increasing the debris carrying ability of the liquid. However, a relatively small amount of debris is actually conveyed to the well surface and removed in this manner because of the relatively large volume of space in a wellbore that must be filled with sand bearing liquid.
Another prior art method for removing debris from a well includes lowering a container into the well which is filled with debris and then removed. Typically, the container is sealed at the well surface and an atmospheric chamber formed therein. When the chamber is lowered into the well and opened, the pressure differential between the interior of the container and the wellbore causes the wellbore contents, like debris to be surged into the container. While this method of debris removal is effective, the amount of debris removed is strictly limited by the capacity of the container and in practice is typically not more than 85% of the chamber volume. Additionally, the container must be continuously lowered into the well, filled due to pressure differential, raised from the well and emptied at the well surface.
More recently, a nozzle or other restriction has been utilized in the wellbore to increase circulation of a liquid and to cause, by low pressure, a suction thereunder to collect or “bail” debris. The use of a nozzle in a pressurized stream of fluid is well known in the art and operates according to the following principles: The nozzle causes pressurized liquid pumped from the surface of the well to assume a high velocity as it leaves the nozzle. The area proximate the nozzle experiences a drop in pressure. The high velocity fluid from the nozzle is diverted out of the tool and the low pressure area creates a vacuum in the tool below the nozzle, which can be used to create a suction and pull debris from a well along with fluid returning to the high velocity stream. By the use of a container, the debris can be separated from the flow of fluid, collected and later removed from the well. A prior art tool utilizing a nozzle and a diverter is illustrated in FIG. 1. The device 100 includes a nozzle portion 105, a diverter portion 110, a container 120 for captured debris and one way valve 125 to prevent debris from returning from the tool to the wellbore 130. A filter is provided above the container but is designed to prevent the passage of particles larger than grains of sand. While the fluid pumped through the nozzle creates a low pressure and suction therebelow, this design is only marginally effective and the suction created in the tool results in only a partially filled container of debris. For example, experiments measuring the effectiveness of the prior art design of FIG. 1 have resulted in a measured suction of only 3–5″ of mercury.
Another apparatus for the removal of debris utilizes a venturi and is described in International Publication No. WO 99/22116 which is incorporated herein in its entirety by reference. The venturi utilizes a nozzle like the one illustrated in prior art FIG. 1. In additional to the nozzle, the venturi includes a throat portion and a diffuser portion to more effectively utilize the high velocity fluid to create a low pressure area and a suction therebelow. The apparatus of the '116 publication, like the device of FIG. 1 also includes a container for holding captured debris wherein the debris enters a flapper valve at the bottom of the container which fills with debris due to suction created by the venturi and is later removed from the well to be emptied at the well surface. While this arrangement is more effective than the one illustrated in FIG. 1, the mechanism is complex and expensive since each part of the device is specially fabricated and the parts are not interchangeable. Most importantly, the nozzle provided with the device is often too small to pass debris carried by the power fluid, clogging the nozzle and making the device useless. Additionally, the size of the container in the prior art devices is fixed limiting the flexibility of the tools for certain jobs requiring large capacity containers.
Aside from simply clearing debris to improve flow of production fluids, debris removal tools can be used to clear debris that has collected in a wellbore over the top of a downhole device, exposing the device and allowing its retrieval and return to the well surface. For example, a bridge plug may be placed in a wellbore in order to isolate one formation from another or a plug maybe placed in a string of tubular to block the flow of fluid therethough. Any of these downhole devices can become covered with debris as it migrates into the wellbore, preventing their access and removal. Removing the debris is typically done with a debris removal device in a first trip and then, in a separate trip, a device retrieval tool is run into the well. This process is costly in terms of time because of the separate trips required to complete the operation.
Debris removal is necessary in any well, whether live and pressurized or dead. In a live well, problems associated with the prior devices are magnified. Circulating fluid through a live well requires a manifold at the well surface to retain pressure within the wellbore. Use of an atmospheric chamber in a live well requires a pressure vessel or lubricator at the well surface large enough to house the atmospheric chambers.
There is a need for debris removal tool utilizing a high velocity fluid stream which effectively removes debris from a wellbore. There is a further need for a debris removal tool that can utilize interchangeable parts depending upon the quality of debris to be removed. There is a further need for a device retrieval tool which can also be used in a single trip to retrieve a downhole device as well as remove debris. There is yet a further need for a debris removal tool with an adjustable container formed of coiled tubing. There is a further need for a method of debris removal and device retrieval in a live well.